EP0382067 and U.S. Pat. No. 5,166,445 describe a preparation method of C15 phosphonic salt by reacting 3,7,11-trimethyldodec-1,4,6,10-tetraene-3-ol with a triarylphosphine and a lower alkanoic acid. During the process, the phosphonic salt of alkanoic acid must be converted into halogenide by anion exchange prior to final Witting reaction. (Z)-phosphonic salt isomers are removed by crystallization process in order to achieve higher E/Z ratio of lycopene, wherein, Z refers to cis-isomer and E refers to trans-isomer, and the following is the same.
EP0895997, U.S. Pat. Nos. 6,187,959, 6,433,226, 6,423,873, 6,603,045 and CN1319600 describe a preparation method of C15 phosphonic salt by reacting 3,7,11-trimethyldodec-1,4,6,10-tetraene-3-ol with a triarylphosphine and strong acids such as sulfonic acid, sulfuric acid, etc., and using a solvent of lower alkanoic acid, wherein a E/Z ratio of the obtained phosphonic salt is between 4˜5:1. A yield of the obtained phosphonic salt is higher than that of C15 phosphonic salt in EP0382067 and U.S. Pat. No. 5,166,445 and the E/Z ratio of obtained phosphonic salt is higher than that of C15 phosphonic salt in EP0382067 and U.S. Pat. No. 5,166,445.
All of the prior patents' methods require use of lots of lower alkanoic acids such as formic acid, acetic acid, or propionic acid as reactant or solvent. But there are two deficiencies: (1) heating and stronger acid are simultaneously in the process, it makes polyene-bonds phosphonic salt contain amounts of undesired impurities and obtain phosphonic salt with deeper color; (2) plenty of organic acid will bring greater process cost, equipment corrosion and environmental pollution.